This project is designed to study biosynthesis, transport and mechanisms of action of steroids involved in the regulation of reproduction. Particular emphasis will be placed on the consequences of interaction between steroids and steroid-binding proteins. This study will be primarily concerned with macromolecular conformational changes which accompany steroid-protein interaction and the significance of these changes in terms of their effects on steroid hormone function. The activity states of enzymes which are affected by steroid binding (at allosteric sites) will be correlated with conformational status. Affinity labeling steroid derivatives will be synthesized and used in the conformational studies and also to assess the topography of steroid binding sites. These derivatives will have the capacity to covalently, and therefore, irreversibly bind at steroid binding sites, and are expected to display long-acting biological activities of a progestogenic or antigestogenic (estrogenic or antiestrogenic) nature. The structure of steroid binding sites on GDH will be examined in terms of amino acid composition, topography, and factors responsible for steroid binding specificity. Purification of selected hydroxysteroid dehydrogenases, steroid isomerases and GDH in which the activity state is altered by steroids will be carried out and utilized in the above studies. Macromolecular conformational dynamics will be studied by integration of spectropolarimetric (ORD/CD), fluorescence spectral difference and ultraviolet spectral difference methods.